1. Field of the Invention
The present invention relates to slide member that has a sliding surface in which microdimples are formed and a method for the production of the slide member. More specifically, the present invention relates to a slide member which has improved slidability under a lubricated condition and a method for the production of the slide member.
2. Description of the Related Art
Conventionally, slide members are used in various devices of a vehicle or the like such as engine and transmission. The use of slide members that have excellent abrasion resistance, low-friction properties and high anti-seizing properties not only ensures the safety of the vehicle but also leads to reduction of carbon dioxide emission from the vehicle for global environmental protection. Thus, various studies on tribology are under way to improve the sliding properties in a sliding condition by improving the surface textures, such as geometry and roughness, of the surfaces of slide members or providing a film that has excellent abrasion resistance and low friction properties on the surfaces of slide members.
As a technique to improve surface textures, a slide member which has a sliding surface in which dimple-like recessions (microdimples) are formed by sandblasting or shot peening and subsequent lapping or barrel polishing has been proposed. In addition, the area ratio of the openings of the microdimples to the entire sliding surface is 5 to 60% in the slide member (refer to Japanese Patent No. 4332977, for example).
As another technique, a slide member is proposed which has a plurality of regularly-arranged fine recesses (microdimples) that are formed by laser radiation in a sliding surface which is lubricated by lubricating oil when the slide member is in sliding motion. The microdimples have an opening area of 10 to 100 square and a maximum depth of 0.1 to 1 μm, and the ratio of total area of the openings of the microdimples to the entire sliding surface is 5 to 30% (refer to Japanese Patent Application Publication No. 2003-184883 (JP-A-2003-184883), for example).
According to the slide member that is described above, the friction coefficient of the slide member can be reduced and the abrasion resistance of the slide member can be improved because the slide member can hold lubricating oil that is supplied onto the sliding surface in the microdimples (recesses) when in sliding motion.
However, the slide member that is disclosed in Japanese Patent No. 4332977 has no regularity in the arrangement of the microdimples because the microdimples are formed by sandblasting or shot peening. Thus, even if the area ratio of the microdimples is increased, the density of the microdimples in the sliding surface may be varied from one location to another. As a result, because the locations where the lubricating oil are held in the sliding surface as a frictional interface are irregularly arranged, local seizure may occur.
In view of these points, it is considered preferable to provide a plurality of microdimples (fine recesses) regularly as in the slide member that is disclosed in JP-A-2003-184883. However, in the case of the slide member that is disclosed in JP-A-2003-184883, the total area ratio of the openings of the microdimples is as small as 5 to 30% and therefore the amount of lubricating oil that can be held in the frictional interface, or the sliding surface, may be too small to improve the anti-seizing properties. In addition, the microdimples are generally circular in shape but it is difficult to arrange the microdimples more densely from the viewpoint of production.
In the production method that is disclosed in JP-A-2003-184883, because the microdimples are formed by laser radiation, the laser emitter or the workpiece is moved by a predetermined distance at a time while the workpiece is processed. Thus, a multiplicity of microdimples cannot be formed simultaneously, and therefore the production of the slide member requires much time and cost.